| Pinus massoniana is a major plantation tree species in southern China,due to its preferable adaptation to the environment and high-quality timber,which played a positive role in the early ecological restoration.However,as most P.massoniana plantations are monocultures,the ecosystem exists many ecological problems,such as fertility declining and pests and diseases increasing,which cannot meet the requirements of social and economic development.Therefore,It is particularly urgent to improve the overall service quality of P.massoniana plantations.Forest gap is the main transformation measures,and its important feature is gap size.The gap size affects the overall service function of the plantation by changing the nutrient cycle within the gap.P.massoniana’s gaps were formed after logging,then Cinnamomum longepaniculatum was planted in each gaps,which is an indigenous tree species with economic value.Based on transformation,the contents of total C,total N,total P and stoichiometric ratio of leaves,litter and soil,the nutrient resorption of C.longepaniculatum in four different gap sizes(G1:10 m×10 m,G2:20 m×20 m,G3:30m×30 m and G4:40 m×40 m),the center and edge of gaps,and different seasons were studied.The results were shown as following:(1)The stoichiometric characteristics of leaves showed that,gap size had significant effects on C,N and P contents and their stoichiometric ratio in leaves.C content showed there is a rising trend with gap size increasing.The maximum value of N content was found in 100 m~2.The minimum value of C:P and N:P were found in 900 m~2.Contents of C,N,P and stoichiometric ratio in leaves were significantly different between center and edge of gaps,excepting for N:P.C content,C:N and C:P in the center which were higher than those in the edge.Meanwhile,the contents of N and P had the oppositive results.Contents of C,N,P and stoichiometric ratio of each season were significantly different.C content and C:N were higher in winter and spring than that in summer and autumn.N content had the maximum value in summer.(2)The stoichiometric characteristics of litter showed that,gap size had significant influence on the contents of C,N,P and their stoichiometric ratio of litter.With the increasing of gap size,the maximum value of litter’s N content was found in 100 m~2.Litter C:N and C:P increased initially and then decreased with the maximum in 400-900 m~2.C,N contents of litter and C:P were significantly affected by sampling position,and the edge was higher than center in general.Sampling time had significant effects on the litter nutrition contents and C:N:P.Litter C content in winter was significantly higher than that in other seasons.The C:N and C:P had the minimum value in spring.(3)The stoichiometric characteristics of soil showed that,gap size had significant effect on the contents of C,N,P and stoichiometric ratio of soil.Soil C,N,P contents and C:N:P increased initially and then decreased with the maximum in 400-900 m~2.The soil each index between center and edge were significantly different,excepting for N:P.The contents of C,N,P,C:N and C:P in gaps’edge were higher than those in center.Seasons had significant influences on the soil nutrition contents and C:N:P.Soil C,N and C:P had the maximum content in summer,and the P content were significantly higher in autumn and winter than that in summer and spring.(4)The study showed that gap size had significant effect on phosphorus resorption efficiency.The maximum value of phosphorus resorption efficiency were found in 400 and900 m~2.Nitrogen and phosphorus resorption efficiency were significantly different between the center and edge,which showed the edge was higher than center.The sampling time had significant effects on the nitrogen and phosphorus resorption efficiency,which were higher in spring than that in other seasons.The phosphorus resorption efficiency were in 9.73-38.78%.The nitrogen resorption efficiency were in 8.76-35.93%.(5)The correlation analysis showed that,there was a significant correlation between the contents of C,N,P and stoichiometric ratio in leaves and litter.The content of P in litter was significantly affected by phosphorus resorption efficiency in leaves.The contents of C and N in leaves and litter,soil C and P contents,C:N and C:P of leaves,litter and soil were mainly affected by soil temperature and soil moisture.In conclusion,gap size have affected the C,N,P stoichiometric characteristics of leaves,litter and soil.C.longepaniculatum is limited by P in this region,and this P limitation in900 m~2 was relieved,which promotes the C.longepaniculatum rapid growth.Therefore,it is suggested that 900 m~2 be used as the size for replanting in P.massoniana plantation.In the study,the leaves,litter of C.longepaniculatum and soil in the gap were taken as a whole to explore the changes of C,N and P stoichiometric characteristics with the increase of gap size.The results are helpful to systematically reveal the nutrient cycling of C.longepaniculatum ecosystem in the gap,and to guide the improvement of the overall service function of P.massoniana plantation in this area. |
PDF Full Text Request